Internal-combustion engines – Combustion chamber means having fuel injection only – Injecting diverse fuels or different states of same fuel
Reexamination Certificate
2000-09-15
2002-10-15
Kwon, John (Department: 3754)
Internal-combustion engines
Combustion chamber means having fuel injection only
Injecting diverse fuels or different states of same fuel
C123S02700A
Reexamination Certificate
active
06463907
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an internal combustion engine operating with a homogeneous charge of combined gaseous and liquid fuel ignited by compression. The present invention further relates to such an engine where exhaust gas is used with the combustible mixture and where gaseous fuel may be used to inject liquid fuel.
BACKGROUND OF THE INVENTION
Current production engines include diesel engines; engines with a homogeneous charge ignited at a particular location as by a spark; and lean burn, spark ignited engines where a locally rich mixture is ignited and provides ignition of an overall lean mixture. These engines are all limited in the maximum efficiency that can be achieved at a given level of emission of nitrogen oxides (NOx) because of the high temperature that is produced in the zone where combustion occurs. In these engines, efficiency is improved by increasing the mean combustion temperature, but this pushes the temperature in the combustion zone into the range in which NOx is generated. This is the case in both the diffusion flame front of a diesel, where the rate of mixing determines the rate of combustion, and in a propagating flame front where the flame travels through a homogeneous or lean charge from a point of ignition. The operation of the above engines will be briefly described as background for Homogenous Charge Compression Ignition (HCCI) engines including HCCI engines embodying the present invention.
More particularly and in diesel engines, only air, with a greater of less admixture of exhaust gas, is compressed in the cylinder, and combustion of a liquid fuel is initiated by heat of compression when fuel is first injected. This combustion continues as the rest of the fuel is injected and oxygen from the air mixes therewith. Conceptually, the same amount of gas is always compressed and, when greater power is required, more fuel is added by injecting fuel over a longer period of time. The efficiency of diesel engines is relatively high because of the high compression ratio, particularly at less than full power where the overall fuel to air ratio is very lean and because the flow of intake gas to the cylinder is not restricted.
It is apparent that, in diesel engines, the fuel should ignite as soon as injection begins; and the cetane number, by which diesel fuels are rated, is a measure of the ease of ignition, a higher cetane number indicating greater ease of ignition.
In the homogeneous charge and lean burn engines, evaporated liquid or gaseous fuel is mixed in an approximately stoichiometric ratio with air before or shortly after the air is provided to the cylinder; the mixture is compressed; and combustion is initiated by ignition, typically by an electric spark, at a point from which the flame front propagates. It is evident that in these engines the fuel should not ignite by compression until the spark occurs so that the fuels used in these engines are relatively difficult to ignite and thus would have a low cetane number. In conventional homogeneous charge engines, the power is controlled by restricting the amount of air provided to the cylinder and varying the amount of fuel provided correspondingly.
It is known to provide a dual fuel variation of the homogeneous charge engine, for example as described in U.S. Pat. No. 3,144,857, which uses an approximately stoichiometric mixture of air and a gaseous primary fuel that can be highly compressed without ignition. This mixture is then ignited at a point, from which the flame front propagates, by a pilot injection of a relatively small amount of diesel fuel that is ignited by compression of the mixture.
It is apparent that, in all of these types of engines, the ignition and start of combustion can be controlled by selecting the point, as an angular position of a crankshaft, where the spark or fuel injection occurs. It is known in some engines of all of these types to employ Exhaust Gas Recirculation (EGR), in which a portion of the gas exhausted from the cylinder is mixed with air being provided to the cylinder. This is typically done to reduce emissions, and complex control arrangements are known for selecting the portion of exhaust gas recirculated in relation to engine load, speed, temperature, amount of oxygen in the exhaust, and the like; these arrangements also selecting related engine control factors such as the time and amount of fuel injected and the time of ignition.
In contrast to the above-described engines, Homogenous Charge Compression Ignition (HCCI) engines produce both very low emissions and diesel engine efficiencies by avoiding the high thermal gradients that are present in either a diffusion or a propagating flame front. In present HCCI engines, an evaporated liquid or a gaseous fuel is mixed with air before or shortly after the air is provided to the cylinder to form a homogenous charge; the mixture ignites as compression continues; and combustion occurs without a defined flame front since combustion is initiated throughout the combustion chamber and the rate of heat release is determined by the chemical reaction rate of the charge.
In HCCI engines, a charge having the same amount of air, with a greater of less admixture of exhaust gas, is always compressed in the cylinder and power is controlled by varying the amount of fuel added to and homogeneously mixed with the charge, with ignition and combustion of the lean mixtures being achieved by high compression ratio and recirculation of hot exhaust gas.
The rapid and homogenous burning possible with HCCI engines has, in concept, the potential to reduce exhaust emissions, retain diesel-like efficiency, and reduce engine cost, particularly in high speed engines. HCCI engines can greatly reduce the level of NOx emissions at a given efficiency due to the more uniform in-cylinder temperature distribution; and, because no flame front is present, the mean cylinder temperature of a HCCI engine is equal to that of a diesel engine without the peak temperature entering the NOx generation region as in the diesel and other engines described above.
HCCI engines should be less expensive to produce than diesel engines or lean burn spark ignited engines since HCCI engines do not necessarily require the high pressure oil system, including pump, distribution system, and injectors of a diesel and do not require the ignition system of a spark ignited engine with spark plugs, spark plug wires, and ignition coils, which offer serious durability problems on heavy duty engines.
Heretofore however, HCCI engines have not been practical because with the previously employed fuels—diesel or natural gas—and arrangements for using these fuels, HCCI engines operate over a limited range of loads and speeds and provide a very low power density—that is, produce a very low amount of power for the displacement and speed of such an engine. These limitations of HCCI engines have resulted from difficulties in controlling the ignition timing of the engine and in producing a long enough combustion event to prevent high peak cylinder pressures.
For the purposes of the present application, the terms “ignition timing” and “ignition delay” are related. Typically, ignition timing refers to the start of desired combustion in relation to a particular angle of crankshaft rotation; and ignition delay refers to the elapsed time before the start of combustion after such an angle, completion of injection of a fuel, or the like. Terms such as “burn duration”, “duration of combustion”, and length of “combustion event” refer to the elapsed time for combustion to be completed after the start of combustion, this elapsed time being measured absolutely or as an angle of crankshaft rotation.
The previously utilized method for selecting the ignition timing of a HCCI engine is by control of Exhaust Gas Recirculation (EGR). That is, the proportion of hot exhaust gas recirculated is increased and the proportion of air is reduced so that the cylinder temperature during compression is increased and ignition delay is shortened. However, the operating speed range of HCCI engines with
Caterpillar Inc
Kwon John
McNeil Michael B.
LandOfFree
Homogeneous charge compression ignition dual fuel engine and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Homogeneous charge compression ignition dual fuel engine and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Homogeneous charge compression ignition dual fuel engine and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2996912